That's a good question to answer with a question.
What does a relay do? Well, what do you want it to do? Don't forget a whole line of protective relays. I fixed 3, 150Y rate-of-rise relays just last week. They have a power supply, balanced input amp, differentiator, threshold comparator, timing circuit, output relay, and an SCR trip circuit. With all that built in, it is still considered a "relay". Don't forget the time delay relays that might keep your compressors from short cycling or give your fan motors a little time to spin down before reversing. That phase loss/reversal/under/over voltage monitor is a relay. I've used bistable impulse relays to replace Hg switches on an alternator table. I think we used a UHF coaxial relay if we had to switch our transmitter into "emergency multiplexing" mode. And finally, I still have to find a use for those stepping relays I picked up at the electronics surplus. They looked like they would be fun to play with at the time.
Joe
